docs: def real_python3(python, version_dict):
      """
      Determine the path of the real python executable, which is then used for
      venv creation. This is necessary, because an active virtualenv environment
      will cause venv creation to malfunction. By getting the path of the real
      executable, this issue is bypassed.
  
      The provided `python` path may be either:
      - A real python executable
      - A virtual python executable (with venv)
      - A virtual python executable (with virtualenv)
  
      If the virtual environment was created with virtualenv, the `sys` module
      will have a `real_prefix` attribute, which points to the directory where
      the real python files are installed.
  
      If `real_prefix` is not present, the environment was not created with
      virtualenv, and the python executable is safe to use.
  
      The `version_dict` is used for attempting to derive the real executable
      path. This is necessary when the name of the virtual python executable
      does not exist in the Python installation's directory. For example, if
      the `basepython` is explicitly set to `python`, tox will use this name
      instead of attempting `pythonX.Y`. In many cases, Python 3 installations
      do not contain an executable named `python`, so we attempt to derive this
      from the version info. e.g., `python3.6.5`, `python3.6`, then `python3`.
      """
      args = [python, '-c', 'import sys; print(sys.real_prefix)']
  
      # get python prefix
      try:
          output = subprocess.check_output(args, stderr=subprocess.STDOUT)
          prefix = output.decode('UTF-8').strip()
      except subprocess.CalledProcessError:
          # process fails, implies *not* in active virtualenv
          return python
  
      # determine absolute binary path
      if os.name == 'nt':  # pragma: no cover
          paths = [os.path.join(prefix, os.path.basename(python))]
      else:
          paths = [os.path.join(prefix, 'bin', python) for python in [
              os.path.basename(python),
              'python%(major)d.%(minor)d.%(micro)d' % version_dict,
              'python%(major)d.%(minor)d' % version_dict,
              'python%(major)d' % version_dict,
              'python',
          ]]
  
      for path in paths:
          if os.path.isfile(path):
              break
      else:
          path = None
  
      # the executable path must exist
      assert path, '\n- '.join(['Could not find interpreter. Attempted:'] + paths)
      v1 = subprocess.check_output([python, '--version'])
      v2 = subprocess.check_output([path, '--version'])
      assert v1 == v2, 'Expected versions to match (%s != %s).' % (v1, v2)
  
      return path